Food slurries such as sauces and purees often contain natural fibers such as cellulose, hemicelluloses, and pectin. High shear processes employing particle size reduction (PSR) equipment such as homogenizers, colloidal mills, sonolators, high shear pumps, and so on reduce the fiber particle size of natural fibers to increase viscosity and texture. Viscosity increases with reduced particle size due to a variety of factors such as increased water holding capacity, pectin dispersion, formation of random three dimensional matrixes of fibers, and pectin entrapment by solutes and water.
Commercial processing techniques used in the processing of fiber-containing food slurries employ a hot PSR operation (e.g., hot homogenization) to improve viscosity and texture (e.g., coarseness) of the slurries prior to cooling of the slurries for cold filling. Cold filling provides many advantages compared to hot-fill-hold or retort-based processes, such as faster cooling rates, reduced cooling water use, the tendency to retain natural product quality and nutrients, and so on.
Tomato slurries are a common type of fiber-containing food slurry that is used in the manufacture of tomato ketchup, tomato puree, tomato sauce, tomato soup, and so on. Conventional tomato processing techniques homogenize tomato slurries at temperatures greater than 140° F. (typically around 180° F.) since the effect of the homogenization pressure at higher temperatures delivers a larger reduction in particle size in the slurry, resulting in a thicker finished product. The viscosity of the homogenized slurries can vary significantly depending on the fiber content, fiber geometry, fiber composition (e.g., hemicelluloses, cellulose, pectin, etc.) as well as complex interactions with formula concentration and operating conditions.
Homogenized food slurries are also generally shear thinning. Therefore, the viscosity of the homogenized slurries is reduced as the material is pumped through pipes, heat exchangers, and so on, which connect the discharge of the homogenizer to the filler apparatus. This loss of viscosity is variable and adversely affects the quality of the finished food slurry.